Events & Seminars

2020 Feb 25

Logic Seminar - Martin Hils

2:00pm to 4:00pm

Location: 

Ross building - Room 63,
Martin Hils will speal about Classification of imaginaries in valued fields with automorphism.


Title: Classification of imaginaries in valued fields with automorphism

Abstract: The imaginaries in the theory ACVF of non-triviallally valued algebraically closed
valued fields are classified by the so-called 'geometric' sorts. This is a fundamental
result due to Haskell-Hrushovski-Macpherson. We show that the imaginaries in
henselian equicharacteristic 0 valued fields may be reduced, under rather general
2020 Mar 24

Matan Seidel (TAU) Random walks on circle packings

2:00pm to 3:00pm

Abstract: A circle packing is a canonical way of representing a planar graph. There is a deep connection between the geometry of the circle packing and the proababilistic property of recurrence/transience of the simple random walk on the underlying graph, as shown in the famous He-Schramm Theorem. The removal of one of the Theorem's assumptions - that of bounded degrees - can cause the theorem to fail. However, by using certain natural weights that arise from the circle packing for a weighted random walk, (at least) one of the directions of the He-Schramm Theorem remains true.
2020 Jan 29

Logic Seminar - Yatir Halevi

9:45am to 11:45am

Location: 

Ross building - Room 63
Yatir Halevi will speal about Coloring Stable Graphs.


Title: Coloring Stable Graphs

Abstract: Given a graph G=(V,E), a coloring of G in \kappa colors is a
map c:V\to \kappa in which adjacent vertices are colored in different
colors. The chromatic number of G is the smallest such \kappa.
We will briefly review some questions and conjectures on the chromatic
number of infinite graphs and will mainly concentrate on the strong
form of Taylor's conjecture:
2020 Jan 22

Logic Seminar - Yuval Dor

11:00am to 1:00pm

Location: 

Ross building - Room 63
Yuval Dor will speal about Transformal Valued Fields.



Abstract:
Abraham Robinson characterized the existentially closed valued fields as those which are algebraically closed and nontrivially valued. This theorem is somewhat surprising: it makes no assumption on the topology of the field other than the fact that it is not discrete, and immediately implies a strong from of the Nullstellensatz, asserting that the only obstruction to the solvability of a system of polynomial equations in a neighborhood of a point is the obvious one.
2020 Jan 30

Groups & Dynamics Seminar. Chloe Perin (HUJI): Homogeneity of torsion-free hyperbolic groups

10:00am to 11:00am

Location: 

Ross 70 a
A countable group is said to be homogeneous if whenever tuples of elements u, v satisfy the same first-order formulas there is an automorphism of the group sending one to the other. We had previously proved with Rizos Sklinos that free groups are homogeneous, while most surface groups aren't. In a joint work with Ayala Dente-Byron, we extend this to give a complete characterization of torsion-free hyperbolic groups that are homogeneous.

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